CN102118174A - I/Q imbalance compensation device in CMMB (China Mobile Multimedia Broadcasting) receiver and method adopting same - Google Patents
I/Q imbalance compensation device in CMMB (China Mobile Multimedia Broadcasting) receiver and method adopting same Download PDFInfo
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Abstract
The invention discloses an I/Q imbalance compensation device in a CMMB (China Mobile Multimedia Broadcasting) receiver. After being input into the imbalance compensation device, two paths of I and Q signals first enter a compensator. According to feedback magnitude and phase error estimation results, Q-path signal compensation is conducted on the basis of the I-path signals. A magnitude estimator calculates power error estimate according to the two paths of I and Q signals. A phase compensator acquires phase error estimate according to the two paths of I and Q signals. A magnitude error loop filter and a phase error loop filter conduct high-frequency error filtration. The loop bandwidth in the loop filters is automatically controlled by a step size controller. The invention also discloses a method for I/Q imbalance compensation in the CMMB receiver. The device and the method can realize fast convergence and high compensation accuracy for the imbalance compensation result of I and Q branch signals, and are suitable for a burst transmission system of CMMB, a fast fading channel environment with channel response changing fast, and the like.
Description
Technical field
The present invention relates to the digital information transmission field, particularly relate to the I/Q branch signal imbalance compensation device among a kind of multi-carrier mobile multimedia broadcasting system CMMB (China Mobile Multimedia Broadcasting, Chinese digital mobile multi-media broadcasting system).The invention still further relates to the method for I/Q imbalance compensation in a kind of CMMB receiver.
Background technology
CMMB is the China Mobile multimedia broadcasting industry standard of China national General Bureau of Radio, Film and Television in October, 2006 promulgation, and this standard was in formal enforcement on November 1 in 2006.CMMB is a kind of wireless broadcast system based on multi-carrier OFDM (OFDM) technology, adopts advanced channel error correction coding and multi-carrier OFDM modulation technique, has improved antijamming capability and to ambulant support; Adopt the time slot radiation pattern to reduce the power consumption of terminal.According to the imagination of the CMMB network coverage, the CMMB signal realizes that by S-band satellite overlay network and U wave band ground overlay network signal covers.S-band satellite network broadcasts channel is used for direct reception, and the Ku wave band is up, and S-band is descending; Distribution channels is used for ground supplement and transmits reception, and the Ku wave band is up, and the Ku wave band is descending, transfers S-band to by ground supplement forwarded device and sends to the CMMB terminal.For realizing effective covering of crowded city mobile multimedia broadcast television signal, adopt the emission of U wave band terrestrial wireless to make up U wave band ground, city overlay network.
Because CMMB is mainly used in portable and portable terminal, the CMMB receiving system is followed the requirement of low-power consumption in design, generally in low-converter Tuner (tuner), use zero intermediate frequency (zero IF) technology, the radiofrequency signal that antenna is received directly changes to the I of zero intermediate frequency, the Q branch signal, this design is low in energy consumption, and it is integrated to be more conducive to chip than the conventional tuner technology, so generally adopt in the CMMB receiving system.But also there is certain technical disadvantages in this zero intermediate frequency technology, because signal is by the I of direct vanishing intermediate frequency, the analog signal of two branches of Q, enter ADC (analog-to-digital conversion) through processing then and become digital signal, to I, can there be certain inconsistency in two branch signals of Q on handling, will make I, and two branch signals of Q produce the imbalance of amplitude and phase place.Such I/Q is uneven to produce significantly influence with recovery to received signal, reduces the quality of reception, as Figure 1-3.Wherein, Fig. 1 is no I/Q imbalance; Fig. 2 has the I/Q imbalance, and is uncompensated; Fig. 3 has the I/Q imbalance, and compensation is arranged.
For the CMMB system,,, be related to the performance of whole receiving system how in the estimation fast and accurately of each data burst section and the unbalanced error of compensation I/Q branch signal owing to be the signal burst transmission.
Summary of the invention
The technical problem to be solved in the present invention provides I/Q imbalance compensation device in a kind of CMMB receiver, makes I/Q branch signal imbalance compensation result convergence and compensation precision height fast; For this reason, the present invention also will provide I/Q imbalance compensation method in a kind of CMMB receiver.
For solving the problems of the technologies described above, I/Q imbalance compensation device comprises in the CMMB receiver of the present invention:
Compensator, be connected with range error loop filter, phase error loop filter, I to input, the Q two paths of signals, range error estimated value according to range error loop filter feedback, with the phase error estimation and phase error value of phase error loop filter feedback, be benchmark with I road signal, carry out Q road signal compensation;
The amplitude Estimation device is connected with compensator, is used to calculate I, the power error estimated value of Q two paths of signals;
Phase estimating device is connected with compensator, and to I, the Q two paths of signals multiplies each other, and obtains the phase error estimation and phase error value;
The range error loop filter is connected with the amplitude Estimation device, filters by the high frequency error in the power error estimated value of amplitude Estimation device input, the range error of the I branch signal that obtains adding up;
The phase error loop filter is connected with phase estimating device, filters by the high frequency error in the phase error estimation and phase error value of phase estimating device input, the phase error of the Q branch signal that obtains adding up;
First step size controller is connected with the range error loop filter, is used for the loop bandwidth of automatic span of control limit of control error loop filter;
Second step size controller is connected with the phase error loop filter, is used for the loop bandwidth of automatic control phase error loop filter.
I/Q imbalance compensation method comprises the steps: in the CMMB receiver of the present invention
Step 2 is by the High-frequency Interference in loop filter difference described phase difference estimation value of filtering and the difference power estimated value;
Step 3, by the variance of step size controller according to the instantaneous signal Error Calculation error in reading signal of loop filter output, with this variance result is criterion, from the step-length pond, select corresponding step value to feed back in the loop filter, carry out the loop filtering of next stage as the convergence bandwidth of loop filter;
Step 4 uses the error result of loop filter output to compensate I, the imbalance of Q two paths of signals.
The present invention is based on the statistical property of received signal, the margin of error by monitoring I, Q two-way branch signal, proposition is the step length command signal of foundation with the variance, the step-length of loop filter when adjusting error compensation automatically by a step size controller, obtain the high I of fast convergence rate and compensation precision, Q two-way branch signal imbalance compensation result, the I/Q unbalanced error of CMMB received signal can be compensated fast and accurately.Effectively overcome the defective that traditional time domain i/q signal imbalance compensation method convergence rate and compensation precision can not be optimized simultaneously; Be particularly suitable for the burst transmission system as CMMB, and the fast-changing fast fading channel environment of channel response.
Description of drawings
The present invention is further detailed explanation below in conjunction with accompanying drawing and embodiment:
Fig. 1-the 3rd, I/Q imbalance and compensation thereof are for the schematic diagram that influences of CMMB received signal;
Fig. 4 is the CMMB receiving system structure chart that comprises I/Q imbalance compensation device;
Fig. 5 is based on the I/Q imbalance compensation device one example structure figure of step-length automatic controller;
Fig. 6 is the control flow chart of I/Q imbalance compensation device.
Embodiment
In order to resist the imbalance distortion on amplitude and phase place of I in the receiver, Q two-way base-band analog signal, before the signal demodulation, need to carry out I, Q imbalance compensation.For the CMMB system, because the signal transmission is divided into 40 time slots, each time slot 25ms each second.Different program streams carries out the time division multiplexing transmission in time in a second, each program stream carries out the signal transmission at predetermined in advance time slot.For certain specific received signal, signal transmission form be 1 second 1 secondary burst, the duration is several time slots, is a kind of burst transfer mode.So just the i/q signal imbalance compensation there is the requirement of convergence rate, needs within a short period of time and finish the error tracking.In addition, because the I/Q imbalance is very obvious for signal demodulation performance influence, the precision that error is followed the tracks of is than higher, otherwise will reduce system's receptivity greatly.
In order to adapt to the communication system of this burst transfer pattern of CMMB, the present invention has adopted a kind of fast convergence rate, and the high I/Q imbalance compensation method of estimated accuracy.This method is based on the statistical property of received signal, the margin of error by monitoring I/Q two-way branch signal, with the variance is to select step-length according to control, the step-length of loop filter when adjusting error compensation automatically by a step size controller obtains the high I/Q branch signal imbalance compensation result of fast convergence rate and compensation precision.
Because I, the imbalance of Q branch signal is a relatively more fixing error, changes very little in time.Therefore can be according to signal long-term statistical computation unbalanced error on time domain.
Fig. 4 is a signal receiving device that meets the CMMB standard, comprising I/Q imbalance compensation device 200.The radio frequency analog signal that receives at first enters a demodulation module 100, produces a baseband complex signal after the data demodulates and comprises a real part I and an imaginary part Q; These two branch signal I, Q enter I/Q imbalance compensation device 200 then, and the complex signal after overcompensation enters a fast fourier transform module 300, and will receive data is frequency domain from spatial transform; Frequency domain data after the conversion enters descrambling module 400 and carries out the data de-scrambling computing; Data after the descrambling enter channel estimation module 500, the channel response of estimated signal in the wireless channel transmission course; Meanwhile, frequency domain data time-delay keep and channel response estimation result synchronously, frequency domain data and channel response estimation result enter channel decoding module 600 afterwards, carry out the channel-decoding processing.
In conjunction with shown in Figure 5, in one embodiment, described I/Q imbalance compensation device 200 comprises: compensator 210, amplitude Estimation device 220, phase estimating device 230, range error loop filter 240, phase error loop filter 250, step size controller 260 and 270.
Behind I, the Q two paths of signals input I/Q imbalance compensation device 200, at first entering compensator 210, according to the amplitude and the phase error estimation and phase error result of feedback, is benchmark with I road signal, carries out Q road signal compensation.I, the Q two paths of signals of compensator 210 outputs enter amplitude Estimation device 220 and phase estimating device 230 respectively.Amplitude Estimation device 220 is according to I, and the Q two paths of signals carries out the calculating of power error estimated value; 230 couples of I of phase estimating device, the Q two paths of signals multiplies each other, and obtains the phase error estimation and phase error value.The instantaneous signal error of amplitude Estimation device 220 and phase estimating device 230 outputs, enter range error loop filter 240 and phase error loop filter 250 respectively and carry out the high frequency error filtration, result after the filtration is the I of statistics, the range error of Q branch signal and phase error.In range error loop filter 240 and phase error loop filter 250, loop bandwidth will be controlled automatically by first step size controller 260 and second step size controller 270.
In conjunction with shown in Figure 6, after system started working, described I/Q imbalance compensation device 200 was in the error trapped state, and the initial step length of loop filter 240,250 is bigger, so loop filter 240,250 output results' variance ratio is bigger.Because continuous two output results' variance can reflect the remainder error of exporting the result, step size controller 260,270 is on this basis as step length command signal; Under the control of variance, step size controller 260,270 is selected bigger loop step-length, carrying out error catches fast, along with dwindling gradually of evaluated error, step length command signal automatically switches to next smaller step size when reaching certain threshold value, and exports to loop filter 240,250, upgrade loop bandwidth, I/Q imbalance compensation device 200 enters the error tracking mode; Because the step-length of loop filter 240,250 reduces, the residue jitter error of estimated result will reduce, when step length command signal reaches next threshold value, step size controller 260,270 continues to switch step value, thereby finally reach an accurate I/Q unbalanced error tracking results SE, referring to formula 1.
SE=(x
i-x
I-l)
2I＞l (formula 1)
Wherein, l is that the data time sequence of participation variance calculating is poor, x
iIt is the instantaneous error value of loop filter output.
The structure and the course of work of step size controller 260,270 are identical, is example below in conjunction with Fig. 5 with the step size controller 260 of range error loop filter 240, specify the structure and the step-length switching controls process of step size controller, can more help to understand the characteristics and the advantage of the quick I/Q imbalance compensation device and method that the present invention is based on the automated variable step size controller.
As shown in Figure 5, first step size controller 260 comprises 262, one step-length ponds 261 of a variance monitor and a step-length selector 263.Variance monitor 262 is connected with the output of range error loop filter 240, receives the instantaneous signal error of range error loop filter 240 outputs, calculates the variance of error in reading signal; This variance can embody the degree of loop convergence, selects the step value of new range error loop filter 240 from step-length pond 261 according to this variance; Variance monitor 262 is opened step-length selector 263 corresponding switches, and new step value feedback is sent into the power error loop filtering computing that the range error loop filter carries out next stage.
Described second step size controller 270 comprises a variance monitor, a step-length pond and a step-length selector; The variance monitor is connected with the output of phase error loop filter, the instantaneous signal error of receiving phase error loop filter output, the variance of calculating error in reading signal; From the step-length pond, select the step value of new phase error loop filter according to this variance; The variance monitor is opened the corresponding switch of step-length selector, and new step value feedback is sent into the phase error loop filter, carries out the phase error loop filtering computing of next stage.
Because the filter effect of loop filter 240,250 is subjected to the influence of loop filtering step-length fully, when step-length was big, the pace of change of its tracking signal was fast, converges faster, but convergence back signal jitter is bigger; When step-length hour, ability that its performance signal changes is relatively poor, tracking velocity is slow, but convergence back signal is more stable, the accuracy height.According to the selection of instantaneous error automatic control loop step-length, can use bigger step-length in an embodiment of the present invention, accelerate convergence rate in the bigger starting stage of error; When the instantaneous error result dwindles gradually, to reselect smaller step size and send into loop filter, the convergence shake of loop filter will be reduced, and improve the accuracy of filtering dateout.Thereby obtain two factors of convergence rate and filtering accuracy simultaneously.
Following simulation result can further embody superiority of the present invention.The I/Q imbalance model that loads on the signal is as follows:
B ' (t)=μ b (t)+vb
*(t) (formula 2)
μ=cos (θ/2)+j α sin (θ/2) (formula 3)
ν=α cos (θ/2)-jsin (θ/2) (formula 4)
Wherein, b is the unbalanced signal of no I/Q, and b ' has the unbalanced signal of I/Q.θ is the unbalance in phase number of degrees, and β is the amplitude imbalance of dB unit.Amplitude imbalance is got ± 3dB, and unbalance in phase is got ± 10 degree.Step-length pond 1 is [2^-5,2^-8].Signal model and channel model are as shown in table 1.
Table 1. simulated conditions
| Signal model | CMMB signal FFT pattern: 4K, constellation pattern: 16QAM, LDPC code check: 2/3 |
| Channel model | Awgn channel, SNR=8.7dB |
Use step-length 2^-5 respectively, 2^-6,2^-7, the variable step size that proposes in the 2^-8 and the embodiment of the invention is carried out the I/Q imbalance compensation.Simulation result shows that the I/Q imbalance compensation of automated variable step-length of the present invention is faster than traditional time domain compensation convergence, and can obtain very high estimation error precision soon; Be fit to very much be applied to burst transmission system, and the fast-changing fast fading channel of channel response.Behind the I/Q imbalance compensation, the CMMB receiving system is obviously improved.Table 2 is its performance comparison result.
Table 2. results of property
Comprehensive the above, the I/Q imbalance compensation device and method based on automatic step-length control of the present invention has following characteristics:
(1) can be automatically according to the step-length of the filter of adjustment loop as a result of error convergence.
(2) carrying out step-length under error output result's variance control switches.
(3) has the step-length pond of the multiple environment of adaptation of a wide region.
More than by specific embodiment the present invention is had been described in detail, but these are not to be construed as limiting the invention.Under the situation that does not break away from the principle of the invention, those skilled in the art also can make many distortion and improvement, and these also should be considered as protection scope of the present invention.
Claims (6)
1. I/Q imbalance compensation device in the CMMB receiver is characterized in that, comprising:
Compensator, be connected with range error loop filter, phase error loop filter, I to input, the Q two paths of signals, range error estimated value according to range error loop filter feedback, with the phase error estimation and phase error value of phase error loop filter feedback, be benchmark with I road signal, carry out Q road signal compensation;
The amplitude Estimation device is connected with compensator, is used to calculate I, the power error estimated value of Q two paths of signals;
Phase estimating device is connected with compensator, and to I, the Q two paths of signals multiplies each other, and obtains the phase error estimation and phase error value;
The range error loop filter is connected with the amplitude Estimation device, filters by the high frequency error in the power error estimated value of amplitude Estimation device input, the range error of the I branch signal that obtains adding up;
The phase error loop filter is connected with phase estimating device, filters by the high frequency error in the phase error estimation and phase error value of phase estimating device input, the phase error of the Q branch signal that obtains adding up;
First step size controller is connected with the range error loop filter, is used for the loop bandwidth of automatic span of control limit of control error loop filter;
Second step size controller is connected with the phase error loop filter, is used for the loop bandwidth of automatic control phase error loop filter.
2. device according to claim 1 is characterized in that: be in the error trapped state earlier after described I/Q imbalance compensation device is started working; The initial step length of two loop filters is bigger, and the variance ratio that obtains according to the instantaneous signal of its output is bigger; Two step size controllers are according to selecting bigger loop step-length, carrying out error and catch fast with the variance; Along with dwindling gradually of evaluated error, when step length command signal reached certain threshold value, two step size controllers automatically switched to next smaller step size, and export to two loop filters respectively, upgrade loop bandwidth, I/Q imbalance compensation device enters the error tracking mode; The step-length of loop filter reduces, and the residue jitter error of estimated result will reduce, and when step length command signal reached next threshold value, two step size controllers continued to switch step value, until finally obtaining an accurate I/Q unbalanced error tracking results.
3. device according to claim 1 is characterized in that: described first step size controller comprises a variance monitor, a step-length pond and a step-length selector; The variance monitor is connected with the output of range error loop filter, receives the instantaneous signal error of range error loop filter output, calculates the variance of error in reading signal; From the step-length pond, select the step value of new range error loop filter according to this variance; The variance monitor is opened the corresponding switch of step-length selector, and new step value feedback is sent into the range error loop filter, carries out the power error loop filtering computing of next stage.
4. device according to claim 1 is characterized in that: described second step size controller comprises a variance monitor, a step-length pond and a step-length selector; The variance monitor is connected with the output of phase error loop filter, the instantaneous signal error of receiving phase error loop filter output, the variance of calculating error in reading signal; From the step-length pond, select the step value of new phase error loop filter according to this variance; The variance monitor is opened the corresponding switch of step-length selector, and new step value feedback is sent into the phase error loop filter, carries out the phase error loop filtering computing of next stage.
5. I/Q imbalance compensation method in the CMMB receiver is characterized in that, comprises the steps:
Step 1, radiofrequency signal and two branch signals of the I that directly changes to zero intermediate frequency, Q of using antenna to receive calculate phase difference estimation value and difference power estimated value respectively;
Step 2 is by the High-frequency Interference in loop filter difference described phase difference estimation value of filtering and the difference power estimated value;
Step 3, by the variance of step size controller according to the instantaneous signal Error Calculation error in reading signal of loop filter output, with this variance result is criterion, from the step-length pond, select corresponding step value to feed back in the loop filter, carry out the loop filtering of next stage as the convergence bandwidth of loop filter;
Step 4 uses the error result of loop filter output to compensate I, the imbalance of Q two paths of signals.
6. method according to claim 5 is characterized in that: according to the selection of instantaneous signal error automatic control loop step-length, in the bigger starting stage of error, use bigger step-length, accelerate convergence rate; When the instantaneous signal error result dwindles gradually, reselect smaller step size and send into loop filter.
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Application publication date: 20110706 |